The present invention relates to internal combustion engines and more particularly to intake arrangements to produce a swirl in each cylinder.
With conventional spark ignited internal combustion engines an intake passageway opening into each cylinder is so designed as to increase the volumetric efficiency of the engine at high speeds under high loads. For this end the passageway has a large cross sectional area, smooth corners and frictionless inner walls to reduce throttling effect, and it is so arranged and positioned, with respect to the cylinder, as to direct the combustible charge at the cylinder axis at an acute angle to and above a plane perpendicular to the cylinder axis. At low speed under light load operating conditions complete mixing of the combustible charge does not take plae and complete combustion takes place only part of the combustible charge and, as a result the conventional internal combustion engine has a high specific fuel consumption and high exhaust emissions at these conditions. At low speed under light load operating conditions when a volume for the combustible charge to be drawn into the cylinder is little, flow velocity of the combustible charge passing through the intake passageway becomes so slow that evaporation of fuel may not occur at a sufficiently high rate and that a swirl with a swirl rate high enough for complete mixing of the fuel with air may not be produced in the cylinder.
This is particularly a problem in the case of a combustion with high exhaust gas recirculation which necessiates sufficient mixing of the charge or, in the case of a combustion with very lean air/fuel mixture.
One possible way to let combustion take place all of the combustible charge in the cylinder at low speed under light load operating conditions is to advance the spark timing at these conditions to compensate for a slow flame propagation through the combustible charge. However, this measure remains problems that the conventional internal combustion engine has a high specific fuel consumption and high exhaust emissions at these conditions unsolved.